Fast,high current electron multiplier having a collector decoupled from ground



June 17, 1969 A. E. GUILLAUME 3,450,921

FAST, HIGH CURRENT ELECTRON MULTIPLIER HAVING A COLLECTOR D'ECOUPLED FROM GROUND Filed Aug. 4, 1966 MEASUP/IVG A PPARA T05 INVENTOR. AAD/PEEI GU/LLAl/Mfi DICEASEI By GEORGES A. BGUTPfAbM/NSTRATA United States Patent 27,18 Int. Cl. H01j 43/00, 39/12, 39/20 US. Cl. 313-104 2 Claims ABSTRACT OF THE DISCLOSURE A fast, high current electron multiplier is disclosed in which a measuring apparatus is included in a signal conducting lead connected to the last dynode and a collector for collecting electrons emitted by the last dynode is decoupled from ground by a capacitor.

The last dynode and collector are disposed within a shield having an opening between the last dynode and the next to the last dynode. The dynodes, collector, and a decoupling capacitor between the collector and ground are all housed within an evacuated envelope.

The present invention relates to an electron multiplier and particularly to a fast high current electron multiplier.

In general in the known electron multipliers, the electrons orginating from the next to the last dynode reach the last dynode after passing a grid in front of it.

This grid serves as a collector for the secondary electrons emitted from the last dynode. The last dynode and the collecting grid in front of it are placed within a focussing shield and the signal is taken from the collector which is connectedto the signal bearing part of the lead to the measuring apparatus, for instance, the central wire of a coaxial cable, the outer part of it being connected to the focussing shield.

These multipliers have the disadvantage that the potential of the collector changes by the signal from the multiplier and this fact introduces a consequent perturbation of the beam of the primary electrons impinging onto the last dynode. An added disadvantage is the necessity to introduce a capacitor outside of the tube in the lead to the measuring apparatus.

It is an object of the invention to provide an electron multiplier with a highly reduced perturbation of the beam of the primary electrons impinging onto the last dynode. It is a further object of this invention to provide an electron multiplier which does not need the introduction of a capacitor in the signal bearing lead to the measuring apparatus.

In accordance with the invention in an electron multiplier, comprising a plurality of dynodes for the multiplication of an electron beam, comprising a collector 3,450,921 Patented June 17, 1969 for the collection of the secondary electrons emitted by the last dynode and comprising means for conducting a signal to a measuring apparatus, these means are connected to the last dynode, and the collector is decoupledfrom ground by a capacitor.

The invention will be described with reference to the accompanying drawing.

The figure shows the last part of an electron multiplier including the collector and the two last dynodes.

In the figure, the dynode 1 represents the next to the last dynode of the electron multiplier. The preceding dynodes are not shown in the figure. Neither are shown the cathode and the enclosure of the multiplier.

The electrons emitted from the dynode 1 reach the last dynode 2 by passing the grid 3 which collects the secondary electrons emitted from the last dynode 2. The dynode 2 and the collector 3 are placed within a focussing shield 4 provided with an opening on the side in front of the dynode 1.

The dynode 2 is connected to the central wire 5 of a coaxial cable, the outer part 6 of it being connected to the focussing shield 4, which is carried by the multiplier structure. The collector 3 is decoupled from this structure by a capacitor 7 disposed within the enclosure of the multiplier and connected to the focussing shield 4.

In this manner the collector 3 is maintained at a fixed potential during operation of the electron multiplier and prevents a strong perturbation of the beam of the primary electrons impinging onto the dynode 2 by constituting a shield between the dynode 2, from which the signal is taken, and the preceding dynodes.

The capacitor 7 is of a classical type, the constituting elements being chosen so as to be able to be incorporated within a vacuum enclosure (mica, copper-nickel, for instance).

To increase the decoupling capacity the elements are grouped in a known manner (not shown in the figure) so as to form a structure of plates pressed together constituting a plurality of capacitors, which can be connected in parallel.

This structure constituting a plurality of capacitors .enables easily decoupling of other electrodes in the electron multiplier susceptible of variations in their potentials by the appearance of a signal in the electron multiplier.

In the embodiment just described, one may for instance apply to dynode 1 a voltage supply of -900 volts and to the collector 3 a voltage supply of +2000 volts. In this case, the focussing shield 4 may have a potential of 0 volt and be connected with the grounded structure of the multiplier. The last dynode may be connected to ground by a resistance. According to this potential the presence of a capacitor in the signal bearing lead to the measuring apparatus is not necessary.

The invention is not limited by the embodiment here described. It is possible to conceive several modifications of the electron multiplier, which remain within the scope of the invention, particularly concerning the relative posi tions of the collector and the last dynode and concerning the use of the focussing shield.

What is claimed is:

1. Electron multiplier, comprising a plurality of dynodes with an evacuated envelope for the multiplication of an electron beam, a collector pervious to the electrons between the last and the next to the last dynodes for the collection of secondary electrons emitted by the last dynode, a shield within which said collector and said last dynode are disposed having an opening therein between said next to the last dynode and the last dynode, means connected to said last dynode for con- 5 ducting a signal to a measuring apparatus, and means decoupling the collector from ground including a capacitor.

2. Electron multiplier according to claim 1 wherein said capacitor is disposed within said evacuated enclosure.

4 References Cited UNITED STATES PATENTS 11/1959 Muench 250207 6/1963 Bush 250207 JAMES W. LAWRENCE, Primary Examiner.

D. OREILLY, Assistant Examiner.

US. Cl. X.R. 

